The present invention relates to an electron microscope having an electron energy loss spectrometer (EELS) called energy filter.
The semiconductor devices and magnetic heads have been miniaturized or small-sized up to laminated thin film structures of a few nanometers (nm) formed on a submicron region. In the device development, it is important to analyze the structures, elementary distributions, crystal structures and chemical bond states of very small regions, and it is also necessary to observe those very small regions at a small magnification so that the whole device structure can be scrutinized at a time.
A Japanese patent document JP-A-2001-93459 (paragraph 0034-0037, FIG. 1) describes a conventional scanning transmission electron. Microscope (STEM) having the energy filter. The conventional electron microscope is described with reference to the conceptual structure diagram of FIG. 6. The electron beam to be irradiated on a sample 5 is deflected by an electron beam-scanning coil 3. For large magnification observation, the electron beam passes along the optical axis of the electron microscope or passes along its vicinity to strike the sample. For small-magnification the electron beam passes not only along the optical axis of the electron microscope or its vicinity but also along paths out of the optical axis. The path of the electron beam passing through a projection lens 7 is corrected by a two-stage deflection coil 8 that is provided on the upstream side of a magnetic sector 9.
In the prior art, when the scanning range of the electron beam at the sample 5 the magnification of an object lens 4, and the magnification of the projection lens 7 are 0.75 μm. 20 and 0.5 respectively, the amount of electron beam shift on the downstream side of the projection lens 7 is 7.5 μm without compensation for the path, and it can be reduced to as low as about 0.5 μm with compensation.
The electron beam having a path compensated by the deflection coil 8 is incident to the magnetic sector 9, where the energy of the electron beam is analyzed. The electron beam exiting from the magnetic sector 9 produces an electron beam energy loss spectrum on the energy dispersion surface of the magnetic sector 9. An electron beam detector 13 measures this electron beam energy loss spectrum. A magnification lens 15 magnifies the electron beam energy loss spectrum, making it possible to examine the shape or the like of the spectrum in details.
When the path of the electron beam is corrected by the prior art, the electron beam is shift by 75 μm at the position of electron beam detector 13. When the energy dispersion is 0.1 eV/25 μm, the amount of shift, 75 μm corresponds to 0.3 eV. However, when the electron beam scans the sample 5 up to a position of 13 μm away from the optical axis of the electron microscope, the electron beam is shifted by 1300 μm at the position of electron beam detector 13. When the energy dispersion is 0.1 eV/25 μm, this amount of shift corresponds to 5.2 eV.
The conventional STEM having the energy filter allows for the compensation for the path of the electron beam up to the incidence to the energy filter from passing through the sample so that the sample can be observed at small magnification. However, since it does not consider the path of the electron beam that exited from the energy filter, the amount of shift increases as described above. Particularly in the above-mentioned document, an electromagnetic lens for magnifying the spectrum is provided on the downstream side of the energy filter, thus eliciting the amount of shift of the energy.